Ozone is a ground-level air pollutant generated primarily by the photochemical reaction of automobile emissions. The primary objective of this research is to determine how anatomical, physiological, and biochemical factors influence the ozone dose that reaches respiratory tissue during a particular exposure condition. The specific aims are to: 1.) Test the hypothesis that an increase in respiratory flow increases the sensitivity of ozone dose to antioxidant levels in the epithelial lining fluid. Ozone absorption will be measured in the nose of healthy nonsmokers at different nasal air flows while antioxidant levels are measured in samples of nasal lining fluid. 2.) Test the hypothesis that the continuous inhalation of ozone and copollutant gases affects antioxidant levels in the epithelial lining fluid, thereby modulating the ozone dose. Respiratory ozone absorption and antioxidant levels in samples of nasal lining fluid will be measured intermittently in the nose of healthy nonsmokers while these subjects are continuously exposed to clean air, ozone, nitrogen dioxide or sulfur dioxide during quite nasal breathing for two hours. 3.) Test the hypothesis that antioxidant concentrations in epithelial lining fluid are directly related to plasma concentrations so that ozone absorption can be modulated by the appropriate pharmacological or dietary interventions. The longitudinal distribution of ozone absorption will be measured throughout the conducting airways of healthy nonsmokers during quite nasal breathing. Measurements will be repeated at baseline conditions, after using probenecid to pharmacologically reduce systemic urate, and after vitamin C supplementation to increase systemic ascorbate. 4.) Quantify the reaction kinetics between ozone and antioxidants in epithelial lining fluid. Samples of nasal lining fluid will be reacted with a controlled flow of ozone in a miniature bioreactor to determine the reaction rate constant and reaction order of ozone concentration. 5.) Further develop the single-path diffusion model. Respiratory absorption as well as in vitro reaction kinetics data will be used to validate a mathematical ozone dosimetry model that can predict the longitudinal distribution of ozone dose to airway tissue.